Empirical Polarization Distribution Models Based on the PARASOL Observations

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a NASA Decadal Survey mission recommended by the National Research Council. CLARREO's objectives are to conduct highly accurate climate change observations and to serve as an on-orbit intercalibration reference for other active instruments by measuring spectral reflectance and monitoring their response function parameters including gain, offset, non-linearity, spectral response of the optics, and sensitivity to polarization. In this presentation we focus on polarization. Polarization effects bias the performance of various currently active spaceborne instruments, such as MODIS and VIIRS, as well as the geostationary imagers. It is essential to evaluate and correct for them in order to perform accurate measurements of various physical quantities such as the total reflectance at the top of the atmosphere. Relative degree of polarization, angle of linear polarization relative to the meridian plane and the instrument's sensitivity to polarization on-orbit fully specify these polarization biases. Based on the 2006 dataset collected by the PARASOL instrument and focusing on the first two quantities we build a global set of the empirical polarization distribution models (PDMs) as function of scene type and viewing geometry. These models will be used by CLARREO to predict the polarization state of the reflected light from the top of the atmosphere and will serve as an intercalibration benchmark for other instruments.